based on a list which I distributed at the Turing Conference in Brighton some years ago, with some further additions. In the Proceedings, Machines and Thought, ed. Peter Millican and Andy Clark, Oxford, 1996, Robin Gandy gives a much earlier reference: Emil L. Post, `Absolutely Unsolvable Problems and Relatively Undecidable Propositions—Account of an Anticipation’, in Martin Davis, (ed.), The Undecidable (New York: Raven Press, 1965), pp.340-435, esp. pp.417-24. Chalmers gives a more up-to-date list in his bibliography—which used to be http://www.artsci.wustl.edu/~philos/papers/chalmers.biblio.4.html but has now moved to Arizona: click here for pursuing his references I am grateful to various correspondents who have helped me to up-date the list given here, and welcome further items.